The present invention relates to an apparatus comprising at least one electrically conductive plastic electrode substantially embedded in a surrounding insulating housing.
Apparatus of this type are known from U.S. Pat. No. 4,368,834, German Patent Application 29 50 039 and U.S. Pat. No. 5,925,830. These devices are configured as electromagnetic flow rate meters and contain two electrodes in diametrically opposing recesses of a tubular housing, which are tightly bonded to the insulating plastic of an internal lining or of the entire tube. The electrodes are made of electrically conductive plastic and, except for the exposed surfaces, which are in contact with the medium flowing through the tube, are enclosed in the insulating plastic. The respective electrode extends radially over the entire thickness of the wall of the housing and/or tube from the inside to the outside and is electrically conductively connected to an electric conductor, which is constructed as a wire or pin in a radially external region. The electric conductor is not enclosed in insulating housing, but rather leads from the radial external surface of the electrode to the outside. According to German Patent Application 29 50 039, a metal mesh is also attached to the electrical conductor and an electrical insulation layer is also provided, the electrically insulating housing also not enclosing the electrical conductor in this case. There is no further information in the three cited publications for other fixing or support of the electrical conductor in relation to the housing. The electrode is exclusively fixed by the housing and additional means for the electrical conductor are not provided. Problems may arise because of this, both in manufacturing, while the electrical conductor and the electrode are pressed in or injection molded, and in use, due to the forces acting on the electrical conductor from the outside, the connection between the electrical conductor and the electrode being disturbed. In addition, the housing, which is configured as a tube, requires a significant amount of space.
An apparatus is known from German Patent 198 45 318, which is configured as an electrochemical oxygen sensor and contains a measurement electrode and an air-oxygen electrode. The measurement electrode comprises a gas-permeable, polymeric, perfluorinated diffusion membrane, which is coated at least partially on one side using a mixture made of a noble metal and PTFE (polytetrafluoroethylene). The diffusion membrane is exposed to the ambient atmosphere and, together with the electrodes described and an electrolyte, is positioned in the sensor housing, which is made of porous PTFE, in order to allow oxygen exchange and pressure equalization independent of position. The measurement electrode and the diffusion membrane are constructed with circular surfaces and have an external diameter of a magnitude of 2 to 50 mm. Since, in such an oxygen sensor, the oxygen must get through the gas-permeable diffusion membrane and the porous housing to reach the inside of the housing to the electrodes positioned there, the possible uses are restricted, use for fluids or mediums which are aggressive and/or under pressure not being possible without something further.
Modern production methods for chemical, biochemical, and pharmaceutical products, food products, or the like react more and more sensitively to changes in the production conditions, so that high precision during the production is necessary. With increasing automation of the production methods, copious information is necessary for detecting the properties of the often aggressive or corrosive fluids or media and the process conditions, this referring above all to the pressure, the temperature, and state of the fluid or medium. To detect information of this type, electrodes are used, which are often positioned directly in the region of the fluid or medium and come into contact with them. Electrical conductors, which must lead out of the region containing the fluid or medium to the outside and/or must be extended through the respective machine or facility parts, are required for using the electrodes and for relaying the information detected to associated electrical or electronic analysis devices.